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-   -   RF interference from TV cable network (http://www.diyaudio.com/forums/digital-source/97422-rf-interference-tv-cable-network.html)

tonvanmil 3rd March 2007 07:54 PM

RF interference from TV cable network
 
Since a few years it is clear to me that whatever DAC you are using it's performance is influenced by many external sources. Of course everybody knows that you have to check polarity of the ac power supply (of all the connected equipment). But have you ever tried what the effect is if you disconnect the antenna input for all your TV or radio equipment in home? You will be surprised.

Particullary the stero imaging is much. much better. The sound has more depth and the staging richer.

Knowing waht the effect is i always disconnect all the antennaplugs in the house for serious listening but this becoming unreasonable with the amaount of sets in the house.

So the question is, does anybody recgonises this problem, and is ther a simple way to get away with it, without having to disconnect all the antennaplugs in the house.

Do I use a ac netfilter for the DAC etc? Yes.

The set I'm using is Audio Note DAC 3 (modified), dual mono preamp (tube), dual mono poweramp (tube 845)

regards
Ton

Netlist 3rd March 2007 08:04 PM

Ton,

I'm most sceptic but admit not having golden ears.
Are you sure you properly terminate the antenna terminals when you unplug the cords?

/Hugo

tonvanmil 4th March 2007 05:48 PM

That;s what I like, sceptism! Yes the wall outlets are terminated. But let's things turn around. Have you already listened to your system wit the TV's and radio's connected and without? Please let me know what the audible effect is in your system.

regards,
Ton

Javin5 4th March 2007 11:32 PM

I just tried this and could not hear any difference. In my quick try, the antenna terminals were not terminated when removing the cord. I have terminals in several rooms, and none of the unused ones are terminated.

Maybe what you experienced has something to do with ground loops? I'm using a small antenna transformer, which galvanically isolates the cable system ground from my HiFi.

Kurt

tonvanmil 5th March 2007 07:05 AM

Kurt,
perhaps your trafo is a solution. What kind of trafo is that? Is it something special or can you buy it everywhere?

Suppose it's a grounding problem, have you an explanation what the path is the "rf signal" followes and "hits" the hifi?

regards,
Ton

Francis_Vaughan 5th March 2007 10:20 AM

Kurt very likely has it in one. There have been some pretty nasty stories about the level of junk that can exist on cable TV feeds - and if you think for a moment about the path the cable takes to your TV, you can see that this is not something you want anywhere near the ground of your system. It is a very big ground loop just waiting to cause grief. Many people have had much worse problems than some difficult to define change in depth and imaging.

A quick set of ideas for DIY isolation is here: http://www.tkk.fi/Misc/Electronics/c..._isolator.html

SY 5th March 2007 10:30 AM

Grounding for sure. In my Heretical Preamp, the major difference I noted was the great improvement from galvanically isolating the cable/satellite grounds from the audio system by using a high quality input transformer.

Jensen Transformer makes a variety of isolation devices, the use of which will save you from having to neurotically run around the house connecting and disconnecting things when you want to change between TV and music.

Javin5 5th March 2007 03:56 PM

Ton, look at the link given by Francis; this is a good article. I was lazy and just purchased a little ground breaker from a local store. Most electronics or HiFi-stores should carry them. You should also get them from online stores, e.g. CONRAD carries two models. They have a rather wide transmission bandwith, so you should be able to use them for FM and TV.

If you have equipment with mains ground (single isolation, 3-pin mains plug) in your HiFi-system, you have a direct connection between the cable ground and the mains ground, which often produces significant hum and other nasties. Here a ground breaker is simply mandatory.

With double insulated equipment (probably the majority of HiFi-gear), you still get some capacitive coupling from the mains supply to the signal ground and thus a current to the cable ground. The effect is smaller here, but it is still advisable to use a ground breaker.

I'm wondering if there is a difference between the cheap ones and the more expensive brands like Jensen. I think they all do a good job as ground breakers, but maybe the sonic quality of some FM-stations could slightly differ?

Kurt

tonvanmil 5th March 2007 07:29 PM

Kurt, Javin,
many thanks. I've just ordered a few galvanic isolation antennamodules. I'm not sure if they're transformer of capacitor coupling devices but we'll see. As soon I've got them you will hear the results. Probably in a few days......... Bye the way, my hifi system has no ac ground.......
regards
Ton


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